[speed_spread]

I would expect plastic and radioactive waste to be our longest lived tell-tale markers, along with stuff we've left on the moon, if anybody ever makes it there again.

[rbanffy]

Millions of years from now, even the devices we left on the moon will be under regolith or mowed down by incoming micrometeorites.

You are probably right that the most obvious signs will look like mineral deposits. Plastic will be back to oil by then.